The Universe Is Speeding Up...

Key Concepts

• Special Theory of Relativity: Einstein's theory stating that nothing can move through space faster than the speed of light.
• Universal Speed Limit: The speed of light (approximately 299,792,458 meters per second), which is the maximum speed for objects moving through space.
• Space Expansion: The phenomenon where the fabric of space itself expands, carrying galaxies and other objects further apart. This expansion is not limited by the speed of light.
• Hubble Sphere: A theoretical sphere centered on an observer, beyond which objects are receding from the observer faster than the speed of light due to the expansion of space.
• Observable Universe: The portion of the universe from which light has had time to reach Earth since the Big Bang, currently estimated to have a radius of about 14 billion light-years.
• GNZ11 Galaxy: A specific, extremely distant galaxy discovered in 2016, used as a prime example of an object receding faster than the speed of light.
• Light-year: A unit of distance representing the distance light travels in one year.

The Universal Speed Limit and Space Expansion

The transcript addresses the apparent contradiction of objects moving faster than the speed of light, given that Einstein's Special Theory of Relativity establishes the speed of light as the universal speed limit. The key clarification is that while nothing can move through space faster than light, space itself can expand. This expansion of space between two objects can cause them to move apart at speeds exceeding the speed of light without violating special relativity. Galaxies are carried along by this expanding space, increasing their separation from each other.

The Hubble Sphere and Distant Galaxies

Our position is considered the center of our observable universe, which extends approximately 14 billion light-years in all directions, forming a sphere. Beyond this sphere lies the Hubble sphere, a region where everything is moving away from us faster than the speed of light due to cosmic expansion. This isn't a minor phenomenon; an astonishing 97% of all galaxies in the universe are currently receding from us at speeds greater than the speed of light.

Observing the Past: The Case of GNZ11

A common misconception is that if something moves faster than light, we would never be able to see it. The transcript clarifies that while we will never see such a galaxy as it is now, we can still observe it as it was when the light left it. This is exemplified by the galaxy GNZ11, discovered in 2016.

• Current Distance: GNZ11 is currently estimated to be approximately 31.96 billion light-years away from us. This implies it is moving away from us at roughly three times the speed of light.
• Observed Past: However, the light we are receiving from GNZ11 left the galaxy 13.4 billion years ago. Therefore, we are seeing the galaxy as it existed in its very early stages.
• Implications: It's a profound thought that GNZ11 might not even exist in its original form anymore; its stars could have burned out, or it might have been absorbed by another galaxy in the intervening 13.4 billion years.

The Expanding Universe and Light Travel

The vast discrepancy between the light travel time (13.4 billion years) and the current distance (31.96 billion light-years) of GNZ11 is explained by the continuous expansion of space. If the universe were static, a light travel time of 13.4 billion years would mean the object is 13.4 billion light-years away. However, as light travels from a distant galaxy like GNZ11 towards us, the space between the galaxy and us is constantly expanding. This expansion stretches the distance the light has to cover, meaning that by the time the light reaches us, the original distance has significantly increased. The light from GNZ11 took 13.4 billion years to reach us, but during that time, the space it traversed expanded, resulting in the galaxy now being much further away than the distance light traveled.

Conclusion

The universe is a dynamic entity where the expansion of space plays a crucial role in how we perceive cosmic distances and speeds. While Einstein's special relativity holds true for objects moving through space, the expansion of space itself allows galaxies to recede from us faster than the speed of light. This phenomenon leads to the existence of a Hubble sphere, encompassing the majority of galaxies, and means that when we observe extremely distant objects like GNZ11, we are essentially looking back in time, seeing them as they were billions of years ago, with their current distances being significantly greater due to ongoing cosmic expansion.